1. Field of the Invention
The present invention relates to a catalyst for removing undesirable materials such as asphaltene, heavy metals, sulfur, and the like contained in heavy hydrocarbon oils by catalytic hydrotreatment whereby said heavy hydrocarbon oils are converted to more valuable hydrocarbon oils.
2. Description of the Prior Art
By the term "heavy hydrocarbon oils" as used in this specification is meant heavy crude oils, residual oils obtained by distilling heavy crude oils under normal pressure or reduced pressure, crude oils extracted from tar sand, and mixtures of these oils. These heavy hydrocarbon oils usually contain undesireable impurities such as so-called asphaltene, i.e., a non-distillable coke precursor which has a high molecular weight and is insoluble in light hydrocarbons such as pentane and heptane; oil-soluble organic metal compounds containing vanadium, nickel, etc.; sulfur compounds; and nitrogen compounds.
These impurities are in most cases contained in high molecular weight hydrocarbon fractions such as asphaltene rendering it very difficult to perform the hydrotreatment of the heavy hydrocarbon oils. By the term "hydrotreatment" as used in this specification is meant the treatment of heavy hydrocarbon oils in the presence of hydrogen and catalysts for (1) converting high molecular weight fractions such as asphaltene contained in the oils into distillable light fractions or fractions soluble in light hydrocarbons and (2) at the same time for removing or reducing the above-mentioned undesirable impurities or contaminants such as metals, sulfur compounds and nitrogen compounds.
At present, as commercial processes for obtaining high-quality light oils by hydrotreating these heavy hydrocarbon oils, there are known processes in which the heavy hydrocarbon oils are subjected to hydrodesulfurization or hydrocracking using a catalyst comprising a transition metal such as cobalt, molybdenum, nickel, or the like, supported on a carrier composed of active alumina such as .gamma.-alumina, .eta.-alumina, or .chi.-alumina, or silica, silica alumina, silica magnesia or the like, in a fixed bed system or ebullating bed system. (T. Ohtsuka, "Catal. Rev., Sci. Eng.", 16(2), 291-325 (1977) and R. V. Driesen, "Preparation of Symposium on Recent Improvements and Developments of Refining Processes and Catalysts", Tokyo, Japan, October, 26-27 (1978)).
However, these processes have the disadvantage that the presence of asphaltene and heavy metals in the feed oils causes various economical disadvantages.
More particularly, since the asphaltene colloidally dispersed in the feed oils is a huge molecule, it does not readily diffuse to the active points in the pores of a catalyst, thus hydrocracking is impeded. Also, the presence of asphaltene accelerates greatly the formation of coke and carbonaceous materials, which results in reducing rapidly the activity of the catalyst.
Furthermore, another difficulty is that the metals which are contained in large amounts in the feed oils accumulate on the surface of the catalyst thereby poisoning the catalyst and considerably shortening its life.
Thus, in the case where heavy hydrocarbon oils are treated by a catalytic hydrotreating process using a conventional catalyst, a large amount of catalyst is consumed per unit amount of oil passed. Moreover, even when the above-mentioned various difficulties can be overcome by these processes, if it is the main object to obtain light oils by causing the selective cracking of asphaltene, the use of a conventional catalyst not only necessitates establishing strict reaction conditions but also promotes deterioration of the catalyst. Moreover, under these conditions the violent gasification of light oils due to their secondary cracking reactions not only makes it difficult to obtain light oils in high yields but also increases the consumption of hydrogen, thus causing a great loss in economy.
In order to overcome these difficulties, various processes have recently been proposed as disclosed in, for example, Japanese Patent Publication Nos. 33,563/76; 42,804/77 and 5212/78. According to these processes, heavy hydrocarbon oils are converted into light hydrocarbon oils by recycling an activated catalyst composed of fine particles of vanadium sulfide, the vanadium sulfide being prepared, for example, by activating vanadium tetrasulfide dispersed in a heavy hydrocarbon oil in the form of slurry or an oil-soluble vanadium compound such as, for example, vanadium resinate mixed with a heavy hydrocarbon oil in a condition of high temperature and high pressure.
Because these processes employ a slurry process using a non-supported vanadium sulfide catalyst it will be easily understood that another serious difficulty will arise in practice. As a typical process for performing a catalytic hydrotreating process at high temperature and high pressure employing a slurry process, a direct liquefication process of coal has been known for a long time. However, it is also known that slurry processes have common problems in that the operation procedure is complicated, troubles such as plugging of passages are liable to occur and specific techniques are required for separating and recovering the fine particles of catalyst from mixture of the catalysts and product oils, so that in order to commercialize these processes, many problems remain to be solved.
Thus, in the prior art it is difficult to perform the catalytic hydrotreatment of heavy hydrocarbon oils containing large amounts of asphaltene and of heavy metals, such as vanadium, in a conventional commercial reactor, such as a fixed bed system, and hence there is a need to develop catalysts which are suitable for the purpose and can maintain a high activity for a long period of time.
The members of a group including the present inventors have made various investigations for a few years to discover catalysts effective for the catalytic hydrotreatment of heavy hydrocarbon oils and free from the deficiencies of the conventional catalysts.
It was discovered that a catalyst comprising one or more transition metals such as cobalt, molybdenum or vanadium supported on a catalyst carrier prepared from inorganic oxides composed mainly of magnesium silicate, in particular, naturally occuring sepiolite, shows high activity and high selectivity for the metal removal of heavy hydrocarbon oils and applications relating to these inventions were filed in the United States. These include U.S. Pat. No. 4,152,250 and U.S. Pat. No. 4,196,102.
Also, it was found that when heavy hydrocarbon oils containing large amounts of asphaltene and heavy metals such as vanadium were subjected to catalytic hydrotreatment using the above-mentioned catalyst, asphaltene was selectively cracked simultaneously with the removal of the metals in the oils (U.S. Patent Application No. 913,114, now U.S. Pat. No. 4,191,636.
The present inventors, who noticed a unique phenomenon on the catalyst in the course of the investigation of the treatment of heavy hydrocarbon oils using the above-mentioned catalyst, have further investigated to develop catalysts which are less expensive and more effective for the hydrotreatment of the heavy hydrocarbon oils.
The unique phenomenon found by the inventors is the interaction between the catalyst carrier composed mainly of naturally occuring magnesium silicate, and the heavy metals and asphaltene contained in heavy hydrocarbon oils that are deposited on the catalysts. This phenomenon results in the catalyst being continuously activated by the accumulations formed on it by the treatment of the oils at high temperature and high pressure in the presence of hydrogen. The inventors have made various experimental investigations of the phenomonon.
As the result, it has been determined that a catalyst comprising vanadium sulfide supported on a specific substrate composed of a naturally occuring mineral clay which consists mainly of magnesium silicate and which has a double-chain structure, which is defined for the Japanese "fukusa-kohzoh" disclosed in page 30 of "Clay Handbook", edited by the Japanese Clay Society in 1967, such as, for example, sepiolite, attapulgite or palygorskite, is very effective for the catalytic hydrotreatment of heavy hydrocarbon oils containing large amounts of asphaltene and heavy metals such as vanadium, and that the catalyst also has a novel characteristic that in the process using the above catalyst, asphaltene is selectively cracked simultaneously with the demetallization and desulfurization and yet the activity of the catalyst can be maintained for a long period of time without being deactivated by the heavy metals which deposit on the catalyst. Based on this knowledge, the invention has been accomplished.